1. Field of the Invention
The present invention relates to an optical disk system, and more particularly to a method of and an apparatus for recording digital image data or other digital non-image data on an optical disk including a magneto-optical disk based on the CWL-CAV (Constant WaveLength-Constant Angular Velocity) principles.
2. Description of the Related Art
Heretofore, it has been customary to record digital data or image and audio data on an optical disk progressively in a radially outward direction. For example, such data are recorded on either one surface of a compact disk (CD) which is 12 cm across or both surfaces of a laser disk which is 30 cm across.
Digital image or non-image data may be recorded on an optical disk according to the CAV (Constant Angular Velocity) process in which the optical disk rotates at a constant rotational speed, the CLV (Constant Linear Velocity) process in which the linear velocity of tracks is constant, or the CWL (Constant WaveLength)-CAV process in which the rotational speed of the optical disk is constant and the recording clock frequency is varied depending on the position of the optical head to record the data at a constant wavelength.
The CAV mode is advantageous because it allows an easy high-speed search process and simple rotational control process, but disadvantageous in that the recording density at radially outer regions of tracks is lowered, making itself inappropriate for high-density data recording. While it is possible to record data at a high density in the CLV mode as the recording density can be constant in all regions of the tracks, the CLV mode results in a time-consuming search process because it is difficult to instantaneously control the disk to rotate at a desired speed when seeking a certain region of the track for playback. The CWL-CAV mode solves these problems, and is capable of attaining the advantages of the CAV mode, i.e., searching for a desired region of the track at a high speed and recording data at a high density.
In the case where a conventional optical disk apparatus is to operate in the CWL-CAV mode, it is necessary to keep the rotational speed of the optical disk constant and vary the recording clock frequency depending on the optical head position for recording desired data on the optical disk. For playback, it is necessary to generate reliably and quickly a playback clock signal in synchronism with reproduced data whose period varies depending on the optical head position. To meet these requirements, the optical disk system operable in the CWL-CAV mode has a complex and expensive circuit arrangement.